title: Structures of CaV2 Ca2+/CaM-IQ domain complexes reveal binding modes that underlie calcium-dependent inactivation and facilitation.
abstract: Calcium influx drives two opposing voltage-activated calcium channel (Ca(V)) self-modulatory processes: calcium-dependent inactivation (CDI) and calcium-dependent facilitation (CDF). Specific Ca(2+)/calmodulin (Ca(2+)/CaM) lobes produce CDI and CDF through interactions with the Ca(V)alpha(1) subunit IQ domain. Curiously, Ca(2+)/CaM lobe modulation polarity appears inverted between Ca(V)1s and Ca(V)2s. Here, we present crystal structures of Ca(V)2.1, Ca(V)2.2, and Ca(V)2.3 Ca(2+)/CaM-IQ domain complexes. All display binding orientations opposite to Ca(V)1.2 with a physical reversal of the CaM lobe positions relative to the IQ alpha-helix. Titration calorimetry reveals lobe competition for a high-affinity site common to Ca(V)1 and Ca(V)2 IQ domains that is occupied by the CDI lobe in the structures. Electrophysiological experiments demonstrate that the N-terminal Ca(V)2 Ca(2+)/C-lobe anchors affect CDF. Together, the data unveil the remarkable structural plasticity at the heart of Ca(V) feedback modulation and indicate that Ca(V)1 and Ca(V)2 IQ domains bear a dedicated CDF site that exchanges Ca(2+)/CaM lobe occupants.
authors.affiliation: Cardiovascular Research Institute, Department of Biochemistry and Biophysics, California Institute for Quantitative Biosciences, University of California, San Francisco, CA 94158-2330, USA.
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Kim
authors.forename: Christine H
authors.initials: CH
authors.lastname: Rumpf
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Fujiwara
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Cooley
authors.forename: Filip
authors.initials: F
authors.lastname: Van Petegem
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Minor
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D002147:Calmodulin / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011817:Rabbits; D051381:Rats; D017386:Sequence Homology, Amino Acid
chemical_list: D002118:Calcium; D020864:Calcium Channels, N-Type; D002147:Calmodulin